Adaptations in human muscle sarcoplasmic reticulum to prolonged submaximal training

Area of Science:

• Exercise Physiology
• Muscle Adaptation
• Cellular Biology

Background:

• Sarcoplasmic reticulum (SR) Ca(2+) handling is crucial for muscle contraction.
• Aerobic training induces various adaptations in skeletal muscle.
• Understanding SR Ca(2+)-regulatory protein changes is key to muscle function.

Purpose of the Study:

• To investigate the effects of 10-week single-leg cycle training on SR Ca(2+)-regulatory proteins and processes in the vastus lateralis.
• To determine specific adaptations in Ca(2+)-ATPase activity, Ca(2+) uptake, and Ca(2+) release.

Main Methods:

• Single-leg submaximal cycle training for 10 weeks (5 sessions/week, 60 min/session).
• Needle biopsy of vastus lateralis 4 days post-training.
• Analysis of homogenate Ca(2+)-ATPase activity, pCa(50), and Hill coefficient.
• Western blot analysis for SERCA1 and SERCA2a protein levels.
• Measurement of SR Ca(2+) uptake and Ca(2+) release.

Main Results:

• Trained leg showed a 19% reduction in maximal Ca(2+)-ATPase activity and a 4.3% increase in pCa(50).
• SERCA1 protein levels were 13% lower in the trained leg; SERCA2a levels remained unchanged.
• SR Ca(2+) uptake decreased by 18%, and SR Ca(2+) release decreased by 26%.

Conclusions:

• Aerobic-based training leads to a downregulation of SR Ca(2+) cycling in the vastus lateralis.
• Reduced Ca(2+)-ATPase activity and SERCA1 protein levels contribute to decreased Ca(2+) uptake.
• These adaptations suggest altered excitation-contraction coupling mechanisms following endurance training.